Wet capacitors are increasingly being used in the design of circuits due to their volumetric efficiency, reliability, and process compatibility. Wet capacitors typically have a larger capacitance per unit volume than certain other types of capacitors, making them valuable in high-current, high power and low-frequency electrical circuits. One type of wet capacitor that has been developed is a wet electrolytic capacitor that includes a valve metal anode, a cathode, and a liquid electrolyte. The unit cell voltage in this type of capacitor is generally higher due to the formation of a dielectric metal oxide film over the anode surface. Wet electrolytic capacitors containing a dielectric from a valve metal tend to offer a good combination of high capacitance with low leakage current. Another type of wet capacitor is a wet symmetric capacitor in which the anode and cathode are similar in terms of structure and composition. The unit cell voltage in this type of capacitor is generally low due to the inevitable decomposition of the electrolyte at high voltage. Whether electrolytic or symmetric, however, the cathodes of wet capacitors have typically included a metal substrate and a conductive coating that provides protection from the liquid electrolyte. Capacitance of the conductive coating is measured through either a faradic current, e.g., electrochemical process or non-faradic mechanism (e.g., double layer formation). Conventional coatings include activated carbon, metal oxides (e.g., niobium dioxide), and the like. Unfortunately, however, the coatings are expensive and can become easily detached under certain conditions.
As such, a need remains for a wet electrolytic capacitor that possesses good thermal, mechanical robustness and electrical performance.